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Thursday, August 12, 2010

I'll be home for dinner (but don't wait up)!

Can snails find their way 'home'? The possibility of a snail homing instinct has long been suspected by, for example, people who want to get rid of snails without killing them so just toss them over the hedge, but a listener to the BBC's Material World program, Ruth Brooks, wanted to actually test the hypothesis. She was chosen by the program last spring as one of four 'amateur scientists' to work with a mentor to try to answer the question.

To do so, she marked a handful of snails from her garden with nail polish and counted how many came back after she had carried them varying distances away from where she'd originally found them. While her experiments are still ongoing, to her science advisor's surprise, her preliminary data (snails are sluggish) suggests that snails placed less than 10 meters away easily return home, though anecdotal evidence she's receiving due to all the media coverage she's getting (on many sites, including on the BBC website) suggests that they can return to a garden from up to a quarter of a mile away.

Ms Brooks and her mentor are now asking anyone in Britain with a garden and a willing neighbor to add data to their database by marking snails from their own garden and swapping them with differently marked snails from their neighbor's garden. (You can follow the experiment on their Facebook page or check it out on the Material Worldwebsite.)

But why was the advisor surprised? As he says, it's because conventional thinking has it that snails are far too simple to do something complicated like find their way home. But this is odd since we all know that 'simple' insects like bees and ants and butterflies very ably find their way home.

It seems to us that this experiment is testing more than the snail homing instinct. It's also testing the testers' preconceived assumptions about the what makes organisms simple and what makes them complex.

Indeed, it's largely our assumptions about what 'simple' organisms can do that makes the exhausting treks of many birds, fish, whales, and insects (like Monarch butterflies) seem so remarkable and truly worth featuring on programs like Discover and Nova. How it works is still largely unknown but magnetic particles in neurons, celestial navigation, and olfaction, seem variably to be part of it. It also seems easy to evolve, since it's happened in parallel, using largely if not entirely different mechanisms and through different media and distances, in so many species.

Probably it's hard for us to imagine because it's so different from our own experience. But a remarkable fact is that we, too, have evolved an uncannily accurate homing mechanism, and we've done it very, very rapidly. It's called a GPS navigator.

10 comments:

Or at least the snail equivalent of 100 miles! Some critics of this experiment are suggesting that those brightly colored snails in all those gardens all over England are now much more visible to anyone who wants garden snail for dinner. Unintended consequences...

Anne makes a key point in science generally. A snail that (who?) doesn't show up at Brooks' garden may not have lost its way. It may have been eaten. That's why the analysis is tricky: we have no idea about the relative probabilities of death to natural causes or being eaten (or run over by a car, or seeing an attractive mate and deciding to move to its locale)

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